As a 30+ year role-playing game aficionado, I love discovering the new and varied systems and tools the community generates every year. However, I am also a fan of some of the original proven systems I played over the years.
Star Trek
I started playing the FASA's Star Trek RPG with my friends around age 14, right after learning about Dungeons & Dragons. I've included the Far Trek RPG (just too good a fan system to pass up), the Star Trek Blueprints Database and the Memory Alpha website. I will say - in my humble opinion - GURPS Prime Directive is something worth looking at for Star Trek campaigns.
RPG Systems and Content
These are just a few of the many, many systems I own, sometimes use for campaigns, and generally enjoy reading through for ideas. While I am certainly partial to GURPS I am also a fan of HERO System, descendant of the one of the earliest super hero role-playing games - Champions. Lately I've been reviewing minimalist or narrative focused game systems, such as Fate and TinyD6.
RPG Tools
The Factory of Heroes is a great program for creating character images. If you like the Bruce Timm art style for your heroes - think Justice League Unlimited - they've duplicated it pretty well here.
Roll20 is a tabletop simulator for RPG. It has an active community and supports many systems with character sheets and paid support materials. It can be utilized for free but if you want enough space for all of your maps and like to keep a lot of games available at one time, there are some paid tiers.
The Star Trek Mini Character Creator is great for cartoonish characters. I used that to generate some character portraits for my TinyD6 Trek adaption.
The World Anvil is something I didn't even know about until now. As a game world designer for many years, albeit stuff I didn't share too much of beyond my players, I am looking forward to using this site to organize and publish some of my game world ideas. They might even prove useful to someone, somewhere, someday.
RPG System Reference Documents (SRD)
Some role-playing game producers have opted to provide their essential rule set as a freely available SRD for the general enjoyment of the community, sans any setting info.